Non-invasive, real time imaging of reporter genes has become an important tool in biomedical applications, including detection of tumors, cell tracking and gene therapy. Here, a versatile, potent technique for targeting, imaging and therapy of tumor cells in culture and in vivo will be evaluated by expressing a single reporter protein (22 kDa) which can be imaged with multiple modalities. First, cell surface receptors will be engineered to efficiently mediate metabolic biotinylation. Second, targeting molecules will include imaging agents for magnetic resonance, optical and positron emission tomography using labeled streptavidin moieties. Third, catalytic domain of diphtheria toxin incorporating streptavidin will be explored to selectively kill tumor cells expressing biotinylated surface receptors. Finally, tumor growth and therapy will be monitored by bioluminescence using tumor cells stably expressing a novel luciferase that is far more sensitive than the ones currently in use. Importantly, these fusion constructs can be easily translated into humans since they are compatible with AAV vectors and the biotin-streptavidin system as well as magnetic nanoparticles and radionuclides are being used in clinical trials. In this project, a new method to target, image, and treat tumors will be explored. First, a virus will be genetically modified to carry a specific DNA sequence (transgene) that once it infects tumor cells in culture and in living mice, it will trigger these cells to produce a specific protein that would make them a selective, easy target for diphtheria toxin, a killing agent, as well as imaging agent for magnetic resonance (MR) and positron emission tomography (PET) therefore only tumors will be imaged and killed.